Field of the Invention
The invention relates to an electrical connection for a power semiconductor component, which is formed inside a baseplate region. The assembly comprises a semiconductor body, a contact clip and a soldered joint which connects the semiconductor body to the contact clip.
U.S. Pat. No. 3,519,896, for example, discloses an electrical connection without any solder, by means of metal clips, for a power semiconductor component. European patent disclosure EP 0 155 473 describes the use of firmly soldered contact clips to make contact with power semiconductor modules.
In power semiconductor components, an electrical supply to a semiconductor body is often formed by a copper layer which is applied on a ceramic substrate. The heat that is produced in the semiconductor body during the operation of the power semiconductor component is also dissipated via the copper layer. Owing to this one-sided heat dissipation and cooling and the temperature drop across the ceramic substrate, which is only a poor heat conductor, power semiconductor components reach their operating temperature in just a few seconds. This is particularly true when they are used in modular form with, for example, a plurality of power semiconductor components being arranged alongside one another.
The fact that the operating temperature is reached quickly means that the power semiconductor components are subject to large numbers of alternating load cycles in many applications, that is to say to a large number of heating and cooling processes. For example, more than 105 alternating load cycles may be reached per annum. Each heating and cooling process, that is to say each alternating load cycle, causes thermomechanical stresses in the power semiconductor component and its electrical supply leads. Large numbers of alternating load cycles can thus cause severe damage in the electrical supply leads on the semiconductor body.
Since the fatigue in the material caused by large numbers of alternating load cycles becomes less the better the coefficient of thermal expansion of the material of the electrical supplies is matched to the coefficient of thermal expansion of the semiconductor body, that is to say the coefficient of thermal expansion of silicon, and of the ceramic substrate, molybdenum or copper-plated Invar is often used as the material for the electrical supplies, and is respectively soldered to the semiconductor body or the ceramic substrate. The use of such materials is disclosed, for example, in the European patent disclosure EP 0 432 867. However, it has been found that there is always a residual mismatch, although this may be small, between the coefficients of thermal expansion of the various materials and, furthermore, mechanical stresses are caused by non-uniform heating of solder connections on the one hand and, particularly with modular construction, of the module base on the other hand. Together with the mechanical stresses, this mismatch leads to slow fatigue in the respective soldered joints between the semiconductor body or the ceramic substrate and electrical supplies.